© 2020 Association for Child and Adolescent Mental Health The recent release of the 11th version of The International Classification of Diseases (ICD-11: WHO, 2018) marked a significant departure from the previous similarities between it and the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; APA, 2013) in terms of their conceptualization of posttraumatic stress disorder (PTSD). The ICD-11 proposed a reduced symptom set for PTSD and a sibling disorder called Complex PTSD. There have been numerous studies that have provided support for the integrity of, and distinction between, PTSD and CPTSD diagnoses in adult samples. Elliot and colleagues (2020) have added to the research literature by providing a valuable examination of the differences between ICD and DSM PTSD/CPTSD in a sample of youth aged 8 to 17 years. This commentary reviews this study and reflects on the need for greater understanding of developmental changes in the presentation of PTSD and Complex PTSD.